1. Field of the Invention
The present invention relates to a liquid crystal display device and a method of manufacturing a liquid crystal display device.
2. Description of the Related Art
Liquid crystal display devices generally have a configuration in which two substrates are disposed to face each other with a predetermined gap (spacing) therebetween, and a liquid crystal is fillingly sealed in the gap between the two substrates to form a liquid crystal layer. In the liquid crystal display thus configured, spacers are interposed between the two substrates so as to hold the gap between the two substrates (the thickness of the liquid crystal layer) at a predetermined size. While fine granular (spherical) spacers have been used, spacers in a columnar shape (hereinafter referred to as “columnar spacers”) have recently come to be used in place of the granular spacers. The columnar spacers are formed on a substrate by use of a photosensitive resin material such as a photo-resist and, hence, they are referred to also as “photo-spacers.”
When a load is exerted on the liquid crystal display device having the columnar spacers in the thickness direction, the substrate and the columnar spacers are deformed under the load. When an excessive load is exerted on a part of the liquid crystal display device, the columnar spacers holding the gap (spacing) between the substrates undergoes plastic deformation at that part. As a result, the gap between the substrates would not return to its initial size even when the load is removed, so that an irregularity in display would be generated.
In recent years, attendant on the reductions in thickness of mobile apparatuses, thinning of glass components in liquid crystal display devices and thinning of the acrylic resin plates or the like covering the surfaces of the liquid crystal display devices have advanced, and there is a tendency toward increased loads being exerted on the liquid crystal display devices. In order to realize a liquid crystal display device with a high pressure resistance under such circumstances, it is effective to enhance the density of the columnar spacers laid out in the substrate surface so as to disperse the pressure exerted on the individual columnar spacers. Specifically, it suffices to increase the area of contact between the substrate and the columnar spacers, either by increasing the number of the columnar spacers laid out per unit area or by enlarging the outer diameter of the individual columnar spacers.
However, the liquid crystal display device generally undergoes a volumetric shrinkage due to a lowering in the density of the liquid crystal under low-temperature environments, so that if the layout density of the columnar spacers is raised by increasing the number of the spacers or by enlarging the spacer outer diameter as above-mentioned, the elastic shrinkage of the columnar spacers may fail to follow up to the volumetric shrinkage of the liquid crystal. Consequently, there may cause a problem on a quality basis in that bubbles are generated in the liquid crystal layer if only a slight impact is exerted on the liquid crystal display device under low-temperature environments. Especially, in mobile use, the liquid crystal display device is frequently exposed to low-temperature environments, and the generation of bubbles would constitute a fatal defect on a quality basis. Therefore, there is a limit to the enhancement of the layout density of the columnar spacers for the purpose of obtaining a higher pressure resistance. In view of this, normally, the retention of quality is given priority over the enhancement of pressure resistance, and the layout density of the columnar spacers is designed to be somewhat low.
In order to solve such a problem, for example, Japanese Patent Laid-open No. 2005-326887 and Japanese Patent Laid-open No. 2002-341354 report a configuration in which two kinds of columnar spacers differing in height are arranged so that the number of the columnar spacers effective in holding the two substrates is varied according to the magnitude of the load (load pressure). In addition, Japanese Patent Laid-open No. 2002-341354 discloses a configuration in which projected stepped parts are formed by stacking layers of substrate-constituting materials, and first columnar spacers are put into contact with the stepped parts, whereby a gap is intermediately provided between second columnar spacers, of which the material and the height are the same as those of the first columnar spacers, and the substrate.